1. Field of the Invention
The present invention relates to a robot control apparatus which controls a robot.
2. Description of the Related Art
Recently, automatically driven robots have often been used. Such robots are driven based on a previously created operation program. During a period in which a robot is operated, the robot sometimes receives a force from outside (hereinafter referred to as “external force”). For example, during a period in which a robot is automatically operated, surrounding equipment or a worker sometimes comes into contact with the robot. In such a case, a robot system is known to stop the robot by detection of an external force or perform an avoiding operation for avoiding a contacted object.
For example, Japanese Laid-open Patent Publication No. H06-155346 discloses a robot teaching apparatus which limits operation of a robot according to an output of a force sensor arranged at a hand portion of the robot. Additionally, Japanese Laid-open Patent Publication No. 2006-21287 discloses a contact force detection apparatus which detects a force applied to a robot arm by arranging a force detector at a root portion of the robot arm. This publication discloses that a control apparatus subtracts an internal force due to operation of the robot arm from the force applied to the robot arm to calculate a contact force applied to the robot arm. In addition, the publication also discloses that an operation of reducing a contact force of the robot arm is performed when the contact force is detected.
A typical industrial robot is configured so that when an external force (a contact force) applied to the robot is detected, an operation program is stopped to ensure safety. In recent years, a robot system has become known in which a worker performs work in collaboration with a robot. This robot system is also designed so that when an external force exceeds a predetermined judgement value, execution of an operation program is stopped.
After a robot is automatically stopped, operation of the robot is preferably restarted in a short time to improve productivity. For example, after a worker contacts with a robot and then the robot is stopped, the worker may immediately step away from the robot. As in this case, when the external force is eliminated after stopping the robot, operation of the robot is preferably immediately restarted.
Alternatively, for example, as in the apparatus described in Japanese Laid-open Patent Publication No. 2006-21287, when the detector is arranged at a base portion of the robot, even vibration of the ground may cause a judgement that an external force has been applied to the robot. For example, when a carrier vehicle travels near a robot, vibration may be transmitted to the robot. Then, the robot may be stopped even when no external force is applied thereto. In such a case, it is preferable to immediately restart operation of the robot.
On the other hand, depending on circumstances at a time of stop of the robot, the stop state of the robot is preferably maintained to ensure safety of the worker. In other words, depending on the kind of external force applied to the robot, it is preferable to maintain the stop state of the robot.